Species Extinction
The biggest effect of over-exploitation is extinction of targeted species. As mentioned in the Over-exploited Species page, there has been rapid decline in certain fish stocks, indicating over-exploitation of these fish stocks (NOAA). If the predicted trajectory of over-exploitation continues, there will soon be no more fishes of certain species. When species goes extinct, you lose an entire library of genetic divergence, thus a loss of biodiversity in the Pacific Northwest (Coleman). |
Trophic Cascades
The phenomenon known as trophic cascade occurs when keystone predators get removed, thus causing a chain reaction affecting the species in the lower trophic levels. After the keystone predator gets removed, this relieves the predatory pressure off the secondary trophic level fishes that the keystone predator usually preys on, causing a rise in its population. This would increase the pressure on the tertiary level fishes, who are prey to the secondary level fishes. This cascade continues on, affecting every trophic level. (Silliman) The consequences of this is a loss in biodiversity. Due to the importance that certain species may have to its ecosystem, this loss in biodiversity can cause regime shifts, in which the whole ecosystem is altered (Mollmann). |
Original Synthetic Figure - Trophic Cascade shows decrease in Tuna population will cause in increase in medium fish populations. Medium fish eats Small fish causing a decrease in Small fish population. This allows Zooplankton populations to increase, overfeeding on Phytoplankton, diminishing their population.
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Bycatch
One of the side-effects of over-exploitation is bycatch. Bycatch occurs when fishermen unintentionally catch fishes and other marine species that they were not targeting in the first place. A majority of these marine animals end up being discarded, left to die or already dead (Oceana). The total estimated amount of bycatch that is discarded in the Pacific Northwest is approximately 9 million metric ton (FAO). Species that are usually affected by bycatch include sea turtles, dolphins, whales, shrimps, birds and a variety of different marine species (FAO). |
Decrease in Overall Fish Size
Commercial fishing selects for larger fish in order to get the most bang for their buck. This means that the fishing industry would rather harvest large fish and generally ignore the small ones. Due to the continuous selective pressure of over-exploitation, all the large fish will eventually die out, leaving just the smaller fish to take their place. The fishing industry will then specifically target these smaller fish because they are considered the "largest" fish by then. This phenomenon is called "Fishing Down" (Pauly, 2009). If over-exploitation continues unchecked, eventually all the fishes in our ocean will be very small! |